Six related sets of experiments are proposed to investigate factors determining choice behavior. The first set of experiments continues our exploration of the relation between choice and rate of reinforcement. In particular, they will help us to assess the effects upon choice of stimulus and response parameters characterizing the interreinforcement intervals being chosen. The second set of experiments continues our work on the transitivity of choice behavior. The proposed research will utilize a new experimental procedure which holds considerable promise for the more efficient and reliable assessment of transitivity. The third set of experiments assesses sequential choice behavior, or behavior on multiple schedules of reinforcement. We propose to study multiple fixed-ratio, fixed-interval, and variable-ratio schedules, particularly as they are affected by component and session duration. We will be especially concerned with interactions obtained in the multiple schedules and in the implications of our data for formulations of behavior on concurrent and multiple schedules that have been developed primarily on the basis of similar experiments with variable-interval schedules. The fourth set of experiments extends our previous work on the hypothesis that the strength of a stimulus, as measured in a choice situation, is a function of the amount of reduction in expected time to reinfrcement signified by the onset of that stimulus relative to the reduction in expected time to reinforcement signified by the onset of the other stimulus. We propose additional experiments to evaluate the generality of this theory of choice and conditioned reinforcement with procedures different from those in which it was developed. Another set of experiments utilizes concurrent schedules to test our hypothesis that second-order schedules of brief stimulus presentations (whether the brief stimuli are paired or unpaired) are more effective in maintaining responding because the brief stimuli effectively block temporal control of responging on the second-order schedules. The final set of experiments assess the strength of elicited responding in a stimulus-reinforcer paradigm and examine the dynamics of interaction between concurrently maintained and topographically tagged elicited and operant responses.